Updating region and availability zone constants (#1810)
Updating region and availability zone constants (#1810)

https://aws.amazon.com/blogs/aws/category/regions/
https://aws.amazon.com/blogs/aws/now-open-aws-middle-east-bahrain/
https://aws.amazon.com/about-aws/whats-new/2019/05/aws-asia-mumbai-adds-third-availability-zone/
cloudtools/troposphere,cloudtools/troposphere